Levothyroxine 25 microgram tablets are a UK-licensed prescription-only oral thyroid hormone replacement. Each tablet contains 25 micrograms of anhydrous levothyroxine sodium, a synthetic form of the natural hormone thyroxine (T4).
Notably, levothyroxine is chemically identical to the T4 your thyroid gland normally makes. So your body handles it exactly as it would natural thyroxine, converting it to the active hormone T3 (triiodothyronine) in tissues as needed.
Multiple UK manufacturers produce levothyroxine tablets: Accord, Teva, Wockhardt, Aristo, Almus, Actavis, and others. The original reference brand was Eltroxin. All UK-licensed generic versions match the reference product for effect, though small differences in bioavailability can occasionally matter for individual patients.
Why 25 microgram is a common starting and titration strength
25mcg has several distinct clinical roles that other strengths don’t cover as well:
Starting dose for elderly patients (usually 60+), where lower starting doses avoid cardiac strain
Starting dose for patients with heart disease (angina, ischaemic heart disease, heart failure, arrhythmias)
Starting dose for long-standing severe hypothyroidism, where slow reintroduction prevents shock to the metabolism
Titration steps between higher doses (adding 25mcg to move from 50mcg to 75mcg, etc.)
Dose combinations: 25mcg alongside 100mcg gives 125mcg total, alongside 150mcg gives 175mcg, and so on
Fine-tuning alternate-day dosing (like 100mcg on 4 days and 125mcg on 3 days for a weekly average of 111mcg)
Maintenance dose for very mild hypothyroidism or subclinical hypothyroidism (where TSH is only slightly raised)
Pregnancy dose adjustment (adding 25mcg to an existing dose)
The 28-tablet pack (one month supply)
The 28-tablet pack provides one month of once-daily dosing. Because levothyroxine is usually a lifelong treatment, monthly pack sizes fit repeat prescription cycles well.
If you take 25mcg once daily as your sole dose, your 28-day pack lasts 28 days exactly. If you take 25mcg alongside another strength (like 100mcg + 25mcg = 125mcg daily), you’ll go through both packs at the same rate.
Why bioavailability and brand matter
Levothyroxine has what pharmacologists call a narrow therapeutic index. In practice, small changes in blood levels can shift you between under-replacement, adequate replacement, and over-replacement. Because different manufacturers formulate their tablets slightly differently, some patients notice symptoms when their pharmacy switches brands.
Key features and details
Active ingredient: anhydrous levothyroxine sodium 25 micrograms per tablet
Class: synthetic thyroid hormone (T4)
Brand: various UK generic manufacturers. Reference brand: Eltroxin
Form: uncoated tablet
Pack size: 28 tablets (one month at once-daily dosing)
Manufacturer: various (Accord, Teva, Wockhardt, Aristo, Almus, Actavis, Concordia)
Legal status: Prescription-Only Medicine (POM)
For: adults, children (with paediatric supervision), and elderly
Primary uses: starting dose in elderly and cardiac patients, titration steps, dose combinations with higher strengths, and mild or subclinical hypothyroidism
Timing: once daily on an empty stomach (30-60 minutes before breakfast, or 2-4 hours after last meal at bedtime)
Storage: below 25°C in original packaging, away from light and moisture
Key features: standard UK treatment for hypothyroidism; titration and starting dose strength; usually part of a lifelong treatment plan
Additional information
Quantity
1 x 28, 2 x 28, 3 x 28
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A prescription-only synthetic thyroid hormone (T4), used to treat hypothyroidism in adults, children, and elderly.
Chemically identical to natural thyroxine, converted by the body to active T3 as needed.
This 25mcg pack: standard starting dose in elderly and cardiac patients, titration steps, dose combinations, and mild or subclinical hypothyroidism.
Usually part of a lifelong treatment plan. Dose adjustments based on regular TSH blood tests.
Extensive drug and food interactions. Pregnancy requires dose adjustment. Available from Courier Pharmacy through our online prescriber service.
Where levothyroxine 25mcg fits in hypothyroidism management
Hypothyroidism management aims to restore normal thyroid hormone levels while avoiding both under-replacement and over-replacement. Because the right dose varies from person to person, most patients need dose adjustments over time based on TSH results and symptoms.
The 25mcg strength plays several distinct roles in this journey. Some patients start on 25mcg and stay there long-term (subclinical hypothyroidism, very small adults, elderly). Others start on 25mcg and titrate up in 25mcg steps over months to their final maintenance dose. Still others take 25mcg alongside higher strengths to build precise daily doses that aren’t available as a single tablet.
Levothyroxine 25mcg vs 50mcg
50mcg is the next step up from 25mcg during titration. Because many patients start on 25mcg (or 50mcg for younger adults without heart disease), the two strengths often get used sequentially. Also, 50mcg is a common maintenance dose for patients with mild hypothyroidism or those with residual thyroid function.
Levothyroxine 25mcg vs 75mcg
75mcg is an intermediate step during titration. So a patient starting at 25mcg might titrate to 50mcg, then 75mcg over several months. Alternatively, 75mcg is built from 50mcg + 25mcg tablets.
Levothyroxine 25mcg vs 100mcg
100mcg is a common maintenance dose for adults with typical replacement needs. Many patients reach 100mcg after titration and stay there long-term. However, 25mcg tablets often still play a role: adding a 25mcg tablet to 100mcg gives 125mcg, a common next step if 100mcg isn’t quite enough.
Levothyroxine 25mcg vs higher strengths (150mcg, 200mcg)
Some patients need higher maintenance doses (150-200mcg), particularly heavier adults, patients after complete thyroidectomy, or those with poor absorption. So 25mcg tablets complement these higher strengths for fine-tuning.
Levothyroxine 25mcg vs oral solution
Levothyroxine oral solution allows very precise dose adjustments in tiny increments (below 25mcg if needed) and suits patients who can’t swallow tablets. However, it’s usually more expensive and less commonly stocked than tablets. So oral solution is reserved for specific situations where tablets don’t fit.
Levothyroxine vs liothyronine (T3)
Some patients ask about T3 (liothyronine) instead of, or alongside, T4 (levothyroxine). Because most patients feel well on levothyroxine alone (as the body converts T4 to T3 as needed), T4 monotherapy is the UK first-line treatment.
However, a small proportion of patients don’t feel fully well on levothyroxine alone. So combination therapy may be considered by specialist endocrinologists in specific circumstances, though NICE currently doesn’t recommend routine combined use.
Alongside supportive lifestyle measures
Levothyroxine works best alongside good general health measures: regular sleep, balanced diet (with adequate iodine, selenium, and other trace nutrients), regular exercise, and managing stress. So even with optimal levothyroxine dosing, energy and wellbeing depend on these other factors too.
Why choose Courier Pharmacy for your Levothyroxine
Specialist endocrinology expertise
Our prescribers have specialist knowledge in endocrinology and so thyroid conditions are a particular area of clinical expertise, alongside general prescribing capability.
This matters because levothyroxine prescribing isn’t just about issuing repeat tablets. Also, it involves reviewing your TSH results, considering interactions with other medicines you take, adjusting doses appropriately in titration or during pregnancy, and identifying situations where you need more thorough investigation.
Registered, independent, and prescriber-led
Courier Pharmacy is a UK-registered independent pharmacy with independent prescribers on-site. The General Pharmaceutical Council regulates us. So when you request levothyroxine through our service, a qualified prescriber assesses your situation before prescribing.
Brand consistency where possible
If you’re sensitive to brand switches, we’ll note your preferred brand and work to keep supplying it. Because MHRA guidance supports brand consistency for sensitive patients, this is standard good practice.
Dr Ada Jex-Cori, our brand pharmacist
Our brand pharmacist is Dr Ada Jex-Cori. She represents the spirit of what we do. Named for Ada Lovelace, Sophia Jex-Blake, and Gerty Cori, she stands for evidence-led, unafraid-of-questions medicine. Her message is straightforward. You’re not broken. The system is. We’re here to change that.
Care that keeps showing up
Levothyroxine is usually a lifelong treatment. So we’re here for the follow-up questions along the way: coordinating TSH monitoring, discussing dose adjustments, managing pregnancy-related changes, troubleshooting interactions, and helping when things aren’t working as expected.
Buy Levothyroxine 25 microgram Tablets from Courier Pharmacy
Levothyroxine 25mcg tablets are a Prescription-Only Medicine. You can request supply through our online prescriber service at courierpharmacy.co.uk.
Complete our online consultation, providing details of your hypothyroidism diagnosis, current dose, most recent TSH result, other medicines you take, and any concerns
Our independent prescriber reviews your case. If levothyroxine 25mcg is appropriate to supply, a prescription is issued
The 28-tablet pack is dispatched promptly, usually next working day
Take exactly as directed on the pack. Keep up with regular TSH monitoring. Contact us if concerns arise or when it’s time for your next repeat
If levothyroxine 25mcg isn’t right for your current situation, we’ll explain why. Options include different strengths of levothyroxine (50mcg, 75mcg, 100mcg for higher doses or dose combinations), levothyroxine oral solution (for those who can’t swallow tablets or need very fine dose control), specific brand requests (Wockhardt, Accord, Teva, Aristo, others), a referral to your GP for TSH testing or dose adjustment, referral to a specialist endocrinologist for complex situations (fertility, pregnancy planning, poor symptom control, suspected T3 conversion issues), or advice on managing coexisting conditions that affect thyroid function.
Above all, we won’t supply levothyroxine when your situation needs proper GP or specialist input first, and we’ll flag when your monitoring or dose review is overdue.
Active ingredient in Levothyroxine 25 microgram Tablets
Anhydrous levothyroxine sodium 25 micrograms per tablet
Levothyroxine sodium is the synthetic form of thyroxine (T4), one of the two main hormones your thyroid gland produces. The 'anhydrous' form means without water, providing a stable, consistent dose in each tablet.
Chemically, levothyroxine is identical to natural thyroxine. Because your body doesn't distinguish between synthetic and natural T4, the effect is the same as if your thyroid were producing this amount itself.
Thyroid hormones T4 and T3
Your thyroid gland produces two main hormones: thyroxine (T4, containing four iodine atoms) and triiodothyronine (T3, containing three iodine atoms). Because T3 is the more biologically active hormone, T4 acts largely as a storage and transport form.
Cells throughout your body convert T4 to T3 as needed, using enzymes called deiodinases. So supplying T4 (levothyroxine) allows your body to make T3 in the right amounts at the right times.
Why T4 (levothyroxine) rather than T3 (liothyronine) as first-line
T4 has a much longer half-life (about 7 days) than T3 (about 1 day). Because this gives smoother, more stable blood levels with once-daily dosing, T4 is the practical first-line choice.
Also, most patients' bodies convert T4 to T3 adequately. So supplying T4 alone lets the body regulate T3 production naturally. Direct T3 therapy causes more fluctuation in blood levels and needs multiple daily doses.
Excipients in Levothyroxine 25 microgram Tablets
Brand-specific excipients
Different UK manufacturers use slightly different excipients. Because these can affect tablet disintegration, absorption, and rare allergic reactions, some patients are sensitive to specific brands.
Common excipients across levothyroxine tablets usually include: microcrystalline cellulose, lactose monohydrate, magnesium stearate, maize starch (or other starch), and sometimes talc, colloidal silicon dioxide, or acacia. Some brands are lactose-free, which matters for lactose-intolerant patients. Check the pack leaflet for the exact composition of your brand.
Lactose content
Many levothyroxine brands contain lactose. So if you're lactose intolerant, ask us about lactose-free brands like Aristo levothyroxine tablets.
What levothyroxine tablets don't contain (varies by brand)
Most brands are gluten-free. However, formulation varies by manufacturer, so check the pack leaflet if this is important to you.
What is Levothyroxine 25mcg for?
Starting dose in elderly patients
For adults over 60 with newly diagnosed hypothyroidism, 25mcg is the standard starting dose. Because older adults are more sensitive to over-replacement and more prone to cardiac side effects, slow introduction protects the heart and gives time for the body to adjust.
Starting dose in cardiac disease
Patients with angina, previous heart attack, heart failure, or serious arrhythmias also start on 25mcg. So this cautious approach avoids precipitating chest pain or arrhythmia that higher doses might trigger.
Titration between doses
25mcg is the standard titration increment. Because most dose adjustments happen in 25mcg steps every 4-6 weeks, this strength is central to the titration process for most patients, regardless of their final maintenance dose.
Dose combinations
25mcg tablets combined with higher strengths let any specific daily dose be built. So a patient on 125mcg takes a 100mcg tablet plus a 25mcg tablet. A patient on 175mcg takes a 100mcg tablet plus a 50mcg tablet plus a 25mcg tablet.
Subclinical hypothyroidism
Subclinical hypothyroidism means TSH is slightly raised but free T4 is still normal. When treatment is decided, starting doses are often 25mcg. So some subclinical hypothyroidism patients stay on 25mcg long-term.
Pregnancy dose increases
Adding 25mcg to a pre-pregnancy dose is a common way to achieve the 25-50% pregnancy increase. For example, a patient on 100mcg pre-pregnancy may move to 125mcg (100mcg + 25mcg) or 150mcg (100mcg + 50mcg) in early pregnancy.
Long-standing severe hypothyroidism
Patients with very high TSH from long-standing severe hypothyroidism start on 25mcg regardless of age. Because their metabolism has adapted to the low-hormone state, rapid full replacement can shock the system.
Very small adults
Very small adults with low body weight (well under 50kg) may need only low maintenance doses. So 25mcg or 50mcg may be the long-term dose.
What levothyroxine 25mcg isn't for
Not for weight loss. Because using thyroid hormone for weight loss in people with normal thyroid function is dangerous (causing heart rhythm problems, bone loss, muscle wasting) and doesn't work sustainably, this use is inappropriate.
Not for tiredness alone without confirmed hypothyroidism. So many other causes of tiredness (iron deficiency, sleep problems, depression, chronic illness) need investigation, not thyroid hormone.
Not for hyperthyroidism (overactive thyroid). This needs different treatment (antithyroid drugs, radioactive iodine, or surgery).
Not for anyone with untreated adrenal insufficiency. Because levothyroxine can precipitate an adrenal crisis in people with adrenal insufficiency, the adrenal problem must be treated first with corticosteroids.
How does Levothyroxine work?
Replacing what your thyroid can't make
Your thyroid gland normally produces T4 (thyroxine) and small amounts of T3 (triiodothyronine). Because these hormones control your body's metabolic rate, cardiovascular function, temperature regulation, brain development, and countless other processes, adequate levels are essential.
In hypothyroidism, your thyroid can't make enough hormone. So levothyroxine tablets provide the T4 externally, restoring normal blood levels.
Absorption from the gut
After swallowing, levothyroxine is absorbed mostly in the small intestine. However, absorption is only about 60-80% at best, and food (particularly high-fibre food, coffee, dairy, and soy) reduces this significantly. So empty-stomach dosing maximises absorption.
Conversion to active T3
Once absorbed, T4 travels in the blood bound to carrier proteins (mostly thyroxine-binding globulin). At the tissues, enzymes called deiodinases convert T4 to the active hormone T3, which then binds to thyroid hormone receptors in cell nuclei.
So levothyroxine works because your body handles it exactly as it handles natural thyroxine. The conversion to T3 happens where and when needed.
Long half-life
Levothyroxine has a half-life of about 7 days. Because this is very long, once-daily dosing produces smooth blood levels, and occasional missed doses don't cause immediate problems. Also, dose changes take 4-6 weeks to fully take effect.
TSH feedback
Your pituitary gland produces TSH (thyroid stimulating hormone) in response to circulating T4 and T3 levels. Because low T4 causes TSH to rise, and adequate T4 causes TSH to fall to normal, TSH is a sensitive marker of thyroid replacement adequacy.
So TSH testing is the main way to monitor and adjust your levothyroxine dose. Free T4 (fT4) is sometimes measured too, particularly in specific situations.
Treatment dosage for Levothyroxine 25 microgram
At a glance
For: hypothyroidism (underactive thyroid) in adults, children (paediatric supervision), and elderly
Starting dose for elderly (60+) or cardiac patients: 25mcg daily
Titration: 25mcg steps every 4-6 weeks based on TSH results
Dose combining: 25mcg alongside 50mcg, 75mcg, 100mcg, 150mcg or 200mcg tablets to build specific daily doses
Timing: once daily on an empty stomach
Duration: usually lifelong
Monitoring: TSH 6-8 weeks after any dose change, then annually when stable
Starting doses in elderly and cardiac patients
For adults over 60, or those with heart disease, the starting dose is 25mcg daily. Because higher doses can strain the heart and precipitate angina or arrhythmias in these groups, the dose is increased slowly (25mcg increments every 4-6 weeks) with careful monitoring.
So many older patients start on 25mcg for their first 4-6 weeks. TSH is then checked. If TSH is still above target, the dose usually increases to 50mcg. This slow, stepwise approach is much safer for the heart than starting on a higher dose.
Starting doses in long-standing severe hypothyroidism
Patients with long-standing severe hypothyroidism (TSH often very high, sometimes above 50 mU/L) may also start on 25mcg regardless of age. Because their metabolism has adapted to the low-hormone state, rapid full replacement can shock the system. So 25mcg starts, followed by slow titration, protects against this.
Titration between doses
Dose adjustments during titration are usually in 25mcg steps every 4-6 weeks. So the 25mcg strength is central to titration, whether alone or combined with other strengths.
For example, moving from 50mcg to 75mcg during titration means adding a 25mcg tablet. Moving from 100mcg to 125mcg also means adding a 25mcg tablet. So even patients ultimately settling on higher doses often use 25mcg tablets to build up.
Dose combinations with higher strengths
Because UK levothyroxine comes in 25mcg, 50mcg, 75mcg, and 100mcg tablets, any dose can be built by combining strengths:
So 25mcg tablets add flexibility for building precise doses that aren't available as a single tablet.
Alternate-day dosing for fine tuning
Some patients need doses between standard tablet strengths, like 87.5mcg or 137.5mcg. So alternate-day dosing achieves this weekly average:
Example: 125mcg on 3 days and 100mcg on 4 days = weekly average of 111mcg
Example: 100mcg on 6 days and 50mcg on 1 day = weekly average of 93mcg
So 25mcg tablets support these alternate-day arrangements as needed.
Subclinical hypothyroidism
Subclinical hypothyroidism means TSH is slightly raised but free T4 is still normal. When treatment is decided, starting doses are often 25-50mcg. So many subclinical hypothyroidism patients only need a low daily dose long-term.
Pregnancy adjustments
Levothyroxine requirements increase by 25-50% during pregnancy. So the 25mcg tablet is the standard tool for adjusting doses during pregnancy. For example, a patient on 100mcg pre-pregnancy may increase to 125mcg (100mcg + 25mcg) once pregnancy is confirmed.
TSH should be checked as soon as pregnancy is confirmed, then every 4 weeks in the first half of pregnancy, then again in the third trimester. So notify your GP or midwife promptly when you become pregnant.
Post-pregnancy step-down
After birth, your levothyroxine dose usually returns to your pre-pregnancy level. So 25mcg reductions are standard steps back down. TSH should be checked at 6 weeks postpartum to confirm the appropriate dose.
Breastfeeding
Small amounts of levothyroxine pass into breast milk, but it's considered safe during breastfeeding. Your dose usually returns to pre-pregnancy levels postpartum.
If you miss a dose
If you miss a dose, take it as soon as you remember (on an empty stomach). However, if it's close to your next scheduled dose, skip the missed one and continue with your normal schedule. Don't double up.
Because levothyroxine has a long half-life (about 7 days), occasional missed doses don't usually cause immediate problems. However, if you regularly miss doses, tell us or your GP so we can help you set up better reminders.
Duration
Hypothyroidism is usually permanent. So levothyroxine is a lifelong treatment for most people. Stopping without medical advice causes hypothyroid symptoms to return within weeks or months.
How to take Levothyroxine 25mcg tablets
Standard use
Take 1 tablet (25mcg) with water, on an empty stomach, once daily. If you're combining with another strength, take both tablets together at the same time.
Swallow whole
Swallow the tablet whole with water. Don't chew or split it unless your prescriber has advised specific splitting. If you have difficulty swallowing tablets, levothyroxine is also available as an oral solution. So ask us for advice.
Empty stomach timing (critical)
Take on an empty stomach. Because food, particularly high-fibre food, coffee, dairy, and soy products, significantly reduces levothyroxine absorption, timing around meals matters more than for most medicines.
Two practical approaches work well:
Morning dose: take with water immediately on waking, then wait 30-60 minutes before eating or drinking anything else (including coffee or tea with milk)
Bedtime dose: take at least 2-4 hours after your last meal or snack. So if you finish dinner at 7pm, take your levothyroxine at 10-11pm before bed
Both work equally well. So choose whichever fits your routine best, and stick with it consistently.
Water only
Take with plain water only. Because coffee (even without milk) reduces absorption by up to 30%, tea (particularly with milk) also reduces absorption, and fruit juices, especially grapefruit juice, can affect the medicine. So water only means water only.
Consistency each day
Take at the same time each day if possible. Because your body reaches steady state on a consistent schedule, timing consistency helps keep blood levels stable between TSH checks.
Combining with other strengths
If your prescription is 25mcg alongside another strength (like 100mcg + 25mcg = 125mcg daily), take both tablets together at the same time on an empty stomach. So the timing is the same whether you take one or several tablets.
Space away from certain medicines and supplements (at least 4 hours)
The following significantly reduce levothyroxine absorption and must be spaced by at least 4 hours:
Iron supplements (ferrous sulphate, ferrous fumarate, Feroglobin, or any multivitamin with iron)
Calcium supplements or calcium-containing antacids (Rennie, Tums, Calcichew)
Aluminium or magnesium antacids (Gaviscon, Maalox, Milk of Magnesia)
Sucralfate
Cholestyramine or colestipol (for cholesterol)
High-dose multivitamins containing iron, calcium, or zinc
Space by 2 hours
The following need spacing by at least 2 hours from levothyroxine:
The following should be avoided at the same meal as your levothyroxine dose:
Coffee (even without milk)
Tea (especially with milk)
Grapefruit juice
Soy products (soy milk, tofu, soy protein powders)
High-fibre supplements (Fybogel, psyllium husk)
Dairy products
Storage
Store the pack below 25°C in the original packaging, away from direct sunlight and moisture. Keep out of reach of children.
Warnings and precautions for Levothyroxine
Adrenal insufficiency must be treated first
Above all, if you have adrenal insufficiency (Addison's disease or hypopituitarism affecting cortisol production), your adrenal problem must be treated with corticosteroids BEFORE starting or increasing levothyroxine. Because levothyroxine speeds up cortisol metabolism, this can precipitate an adrenal crisis in undiagnosed or untreated adrenal insufficiency.
So screening for adrenal function is essential in patients with hypopituitarism, autoimmune conditions, or symptoms suggestive of adrenal problems.
Cardiovascular disease
Patients with angina, previous heart attack, heart failure, or serious arrhythmias need very careful dose introduction. Because rapid dose increases can precipitate chest pain, arrhythmias, or heart failure worsening, starting doses of 25mcg with slow 25mcg increments every 4-6 weeks are essential.
So the 25mcg strength is specifically important in this group. Also, cardiac symptoms during titration need urgent assessment.
Elderly patients
Older adults are more sensitive to over-replacement and more prone to atrial fibrillation from higher doses. So starting doses of 25mcg with slow adjustments protect against these problems. Also, TSH targets are often slightly higher than in younger adults.
Long-standing severe hypothyroidism
Patients presenting with very high TSH from long-standing severe hypothyroidism need cautious dose introduction regardless of age. Because their metabolism has adapted to the low-hormone state, rapid full replacement can cause chest pain, palpitations, or cardiac events. So 25mcg starts protect against this.
Diabetes
Starting or adjusting levothyroxine can affect blood glucose control in diabetes. Because thyroid hormone increases glucose absorption and insulin needs, insulin or oral antidiabetic drug doses may need adjustment. So more frequent blood glucose monitoring is helpful during levothyroxine dose changes.
Diabetes insipidus
Levothyroxine can occasionally worsen diabetes insipidus. So specialist input is useful in this rare situation.
Pregnancy
Levothyroxine is safe in pregnancy. However, dose requirements usually increase by 25-50%. So notify your GP or midwife as soon as pregnancy is confirmed, and expect TSH monitoring every 4 weeks in early pregnancy.
Breastfeeding
Levothyroxine is safe in breastfeeding. Small amounts pass into breast milk but not enough to affect the baby's thyroid function.
Long-term over-replacement risks
Persistently taking too much levothyroxine (TSH suppressed below normal) increases risk of:
Atrial fibrillation (particularly in elderly)
Osteoporosis (particularly in postmenopausal women)
Muscle weakness
Anxiety and insomnia
So regular TSH monitoring aims to keep levels in target and avoid over-replacement.
Signs of over-replacement
Report to us or your GP promptly if you notice: palpitations, fast heart rate, tremor, unusual sweating, heat intolerance, weight loss, anxiety, insomnia, or diarrhoea. So these suggest your dose is too high.
Signs of under-replacement
Report if you notice worsening tiredness, weight gain, cold intolerance, constipation, brain fog, hair thinning, muscle aches, or low mood. So these suggest your dose may be too low, particularly important during titration from 25mcg upwards.
Signs of severe allergic reaction
Allergic reactions to levothyroxine itself are extremely rare. However, some patients react to tablet excipients (particularly lactose or specific colouring agents in some brands). Symptoms of severe allergic reaction include rash, facial swelling, breathing difficulty. Call 999 if severe.
Alcohol
Moderate alcohol doesn't interact with levothyroxine. So normal social drinking is fine.
Driving and machinery
Levothyroxine doesn't affect driving or machinery use at appropriate doses. However, unrecognised over-replacement can cause tremor and anxiety that affects concentration.
Side effects of Levothyroxine
Side effects mostly relate to over-replacement
At appropriate doses matched to your body's needs, levothyroxine has few side effects because it's replacing a natural hormone. However, if your dose is too high (over-replacement), symptoms of hyperthyroidism appear.
Notably, on a 25mcg starting dose, over-replacement symptoms are less common than at higher doses. However, they can still happen, particularly in very sensitive patients or if TSH suppresses rapidly.
Symptoms of over-replacement
These include:
Palpitations, fast heart rate
Tremor (particularly in hands)
Anxiety, restlessness, irritability
Difficulty sleeping
Sweating, feeling hot, heat intolerance
Unexplained weight loss
Diarrhoea
Menstrual irregularities in women
Muscle cramps or weakness
Chest pain (particularly in older patients or those with heart disease)
So if you notice these, contact us or your GP for TSH testing. Also, dose reduction usually resolves symptoms within a few weeks.
Symptoms of under-replacement
On a starting dose of 25mcg alone, some symptoms of hypothyroidism may still be present or slow to improve. So this is expected during titration, and TSH testing at 6-8 weeks will guide dose adjustment upward.
Symptoms include:
Continuing tiredness
Weight gain not improving
Feeling cold, cold intolerance
Constipation
Dry skin, hair thinning
Brain fog, poor concentration
Low mood, depression
Muscle aches
So report these too, particularly if you've been on 25mcg for 6+ weeks without dose review.
Rare allergic reactions
Levothyroxine itself is chemically identical to natural thyroxine, so true allergy is extremely rare. However, some patients react to specific tablet excipients (lactose, colouring agents). So switching to a different brand often resolves excipient-related sensitivities.
Symptoms of severe allergic reaction: rash, hives, facial or throat swelling, breathing difficulty. So stop taking and call 999 for severe reactions.
Long-term risks from over-replacement
Long-term over-replacement (TSH suppressed below normal) can cause:
Atrial fibrillation (particularly in elderly)
Osteoporosis and fracture risk (particularly in postmenopausal women)
Loss of muscle mass
So regular TSH monitoring helps avoid this by keeping doses in target.
Serious side effects requiring urgent help
Above all, seek urgent medical help for signs of severe allergic reaction (facial or throat swelling, breathing difficulty), chest pain, severe palpitations or dizziness, or signs of adrenal crisis (severe weakness, dizziness, low blood pressure, salt cravings). Call 999 if severe.
Report any suspected side effects to the MHRA Yellow Card scheme at yellowcard.mhra.gov.uk or via the Yellow Card app.
Drug interactions with Levothyroxine
Iron supplements
Iron significantly reduces levothyroxine absorption. So space by at least 4 hours between your levothyroxine and any iron-containing product (ferrous sulphate, ferrous fumarate, Feroglobin, most multivitamins with iron).
Calcium supplements
Calcium reduces levothyroxine absorption. So space by at least 4 hours from calcium supplements or calcium-containing antacids like Rennie, Tums, or Calcichew.
Aluminium and magnesium antacids
Antacids containing aluminium or magnesium (Gaviscon, Maalox, Milk of Magnesia) reduce levothyroxine absorption. So space by at least 4 hours.
PPIs (proton pump inhibitors)
PPIs like omeprazole, lansoprazole, esomeprazole, pantoprazole, and rabeprazole reduce stomach acid. Because levothyroxine absorption depends partly on stomach acid, PPIs can reduce levothyroxine effectiveness. So separating doses by 2+ hours can help.
Warfarin
Levothyroxine can enhance warfarin's anticoagulant effect. So INR should be monitored more closely when starting, stopping, or changing levothyroxine dose.
Diabetes medications
Starting or increasing levothyroxine can raise insulin or oral antidiabetic drug requirements. So closer blood glucose monitoring helps during dose changes.
Digoxin
Levothyroxine can reduce digoxin's effect. So digoxin levels may need monitoring.
Estrogens (HRT, combined oral contraceptives)
Estrogens increase thyroxine-binding globulin, raising bound thyroxine levels. Because this can effectively lower free (active) thyroxine, some patients need levothyroxine dose increases when starting estrogens. So TSH check 6-8 weeks after starting or stopping estrogens is helpful.
Antiepileptics
Carbamazepine, phenytoin, and phenobarbital increase levothyroxine metabolism. So dose increases may be needed.
Rifampicin
Rifampicin (used for tuberculosis and other infections) increases levothyroxine metabolism. So dose increases may be needed.
Ritonavir (MHRA 2018 alert)
An MHRA alert flagged interaction between ritonavir-containing HIV medications and levothyroxine, leading to reduced thyroxine levels. So HIV specialists usually manage this combination.
Amiodarone
Amiodarone has complex effects on thyroid function (can cause both hypothyroidism and hyperthyroidism). So patients on amiodarone need specialist thyroid function monitoring.
Lithium
Lithium can cause hypothyroidism. So thyroid function needs monitoring in patients starting lithium, and levothyroxine may be needed.
Cholesterol medications
Cholestyramine and colestipol reduce levothyroxine absorption. So space by at least 4 hours.
Sucralfate
Sucralfate (for peptic ulcers) reduces levothyroxine absorption. So space by at least 4 hours.
Beta-blockers
Propranolol may reduce conversion of T4 to T3 at high doses. However, standard doses don't usually cause clinically significant problems.
Food and drink interactions
These reduce absorption if taken at the same time:
Coffee (even without milk) reduces absorption by up to 30%
Tea (particularly with milk)
Grapefruit juice
Soy products (soy milk, tofu, soy protein powders)
High-fibre foods and fibre supplements
Dairy products
Alcohol
Moderate alcohol doesn't directly interact with levothyroxine.
Frequently asked questions about Levothyroxine 25mcg
Who takes 25mcg of levothyroxine?
Elderly patients starting treatment, cardiac patients starting treatment, patients with long-standing severe hypothyroidism starting treatment, patients being titrated up (25mcg is the standard titration step), patients combining strengths for specific doses (like 125mcg = 100mcg + 25mcg), and some patients with subclinical hypothyroidism who need only a low daily dose.
Is 25mcg a maintenance dose?
For some patients yes, particularly those with subclinical hypothyroidism, very small adults, or elderly patients with mild disease. However, for most adults with typical hypothyroidism, 25mcg is a starting or titration dose rather than a long-term maintenance dose.
How do I take levothyroxine?
Once daily on an empty stomach. Either 30-60 minutes before breakfast, or at bedtime 2-4 hours after your last meal. Take with water only. Consistency each day matters.
Why empty stomach?
Food, especially high-fibre foods, coffee, dairy, and soy, significantly reduces levothyroxine absorption. So empty-stomach dosing can improve absorption by up to 40%.
Can I take with coffee?
No. Coffee (even without milk) reduces levothyroxine absorption by up to 30%. So wait at least 30-60 minutes after your dose before having coffee or tea.
What if I miss a dose?
Take it as soon as you remember (on an empty stomach). However, if it's close to your next dose, skip the missed one and continue with the normal schedule. Don't double up. Occasional missed doses aren't usually a problem because of levothyroxine's long half-life.
How long will I stay on 25mcg?
This depends on your specific situation. If you're starting treatment and titrating up, 25mcg is usually just the first few weeks before your dose increases. If you have subclinical hypothyroidism or mild disease, 25mcg may be your long-term dose. So your TSH results and symptoms guide the answer.
How often will I need blood tests?
TSH is checked 6-8 weeks after starting or after any dose change, then usually annually once stable. During titration, more frequent checks may be needed. During pregnancy, expect testing every 4 weeks in early pregnancy.
What's my TSH target?
Generally 0.4-4.0 mU/L for most adults, though targets are individualised. In pregnancy, aim for below 2.5 mU/L in first trimester and below 3.0 mU/L in second and third trimesters.
Can I combine 25mcg with a higher strength?
Yes. Because UK levothyroxine comes in 25mcg, 50mcg, 75mcg, and 100mcg strengths, dose combinations build any specific total: 125mcg = 100mcg + 25mcg, 150mcg = 100mcg + 50mcg, 175mcg = 100mcg + 50mcg + 25mcg, and so on.
What about brands?
Different UK brands (Accord, Teva, Wockhardt, Aristo, Almus, and others) contain the same active ingredient. However, some patients notice symptoms after brand switches. So MHRA guidance supports brand consistency for sensitive patients.
Can I take levothyroxine during pregnancy?
Yes, and you should continue treatment. However, your dose usually needs to increase by 25-50% in early pregnancy. So notify your GP or midwife as soon as you become pregnant, and expect TSH monitoring every 4 weeks initially.
Can I take levothyroxine while breastfeeding?
Yes. Small amounts pass into breast milk but not enough to affect the baby.
What if I take iron or calcium supplements?
Space these by at least 4 hours from your levothyroxine dose. So if you take levothyroxine in the morning, take your iron or calcium at lunchtime or later.
What if I take a PPI (omeprazole, lansoprazole)?
PPIs can reduce levothyroxine absorption. So separating doses by at least 2 hours helps, and your prescriber may check TSH more often if you take both long-term.
Can I use levothyroxine for weight loss?
No. Levothyroxine for weight loss in people with normal thyroid function is dangerous and doesn't work sustainably. So it's only appropriate for people with confirmed hypothyroidism.
What are the signs I'm taking too much?
Palpitations, fast heart rate, tremor, unusual sweating, heat intolerance, weight loss, anxiety, insomnia, or diarrhoea. So contact us or your GP for TSH testing if you notice these.
What are the signs my dose needs to increase from 25mcg?
If hypothyroid symptoms haven't improved after 6-8 weeks on 25mcg (continuing tiredness, weight gain, cold intolerance, brain fog), or if TSH is still above target on repeat testing, your dose needs to increase. So this is expected during titration.
Can I take levothyroxine with other medicines?
Many other medicines can be taken alongside levothyroxine, though timing matters for some (iron, calcium, PPIs). So tell us and any other healthcare providers about every medicine you take.
What if I have heart disease?
25mcg is specifically the starting dose for cardiac patients. So this pack fits directly. Dose adjustments need to be made more slowly if you have angina, previous heart attack, or heart failure, and cardiac symptoms during titration need urgent assessment.
Do I need a prescription?
Yes. Levothyroxine is a Prescription-Only Medicine (POM). So our online prescriber service can supply repeat prescriptions after assessment, or refer you back to your GP or a specialist if needed.
How should I store levothyroxine?
Below 25°C in the original packaging, away from direct sunlight and moisture. Keep out of reach of children.
What if I need to travel?
Bring your levothyroxine in original packaging. Because time zone changes matter less over a few days (thanks to levothyroxine's long half-life), take at your usual home time until you settle into local time on longer trips.
Disclaimer
Disclaimer: This information is for education only and isn't a substitute for personal medical advice. Levothyroxine is a Prescription-Only Medicine and should only be taken when prescribed after clinical assessment. It's not intended to diagnose, treat, cure, or prevent any condition without prescriber assessment. Always follow the pack directions and your prescriber's specific instructions. Regular TSH monitoring is essential. Contact your prescriber, GP, or A&E urgently for signs of adrenal crisis (severe weakness, dizziness, low blood pressure), chest pain, severe palpitations, or signs of severe allergic reaction. Levothyroxine should never be used for weight loss in people without confirmed hypothyroidism.
References
National Institute for Health and Care Excellence (2019, updated 2023) Thyroid disease: assessment and management. NG145. Available at: https://www.nice.org.uk/guidance/ng145
